The invention provides circuits and methods for estimating and correcting
nonlinear error in analog to digital converters that is introduced by
nonlinear circuit elements, for example one or more residue amplifiers in
a pipelined analog to digital converter integrated circuit. In a
preferred method of the invention, pseudo random calibration sequences
are introduced into the digital signal to be converted by a flash digital
to analog converter in one or more initial stages of the pipelined analog
to digital converter circuit. A digital residue signal of the output of
the one or more initial pipelined analog to digital converter stages is
sampled. Intermodulation products of the pseudo random calibration
sequences that are present in the digital residue signal are determined
to estimate nonlinear error introduced by the residue amplifier in the
one or more stages. A digital correction signal is provided to the output
of the one or more stages to cancel estimated nonlinear error.